A YouTube video posted by f1ipzid3 shows a side-by-side comparison between the iPhone 5 and iPhone 4S video taking abilities.
Comparing the video shots from the iPhone 5 vs. iPhone 4s
This video looks at indoor and outdoor light, front and rear camera, depth of field & also notice the difference in stabilization.
Both iPhones were handheld on top of one another to have equal comparison
All Video has not been altered other than cropping/sizing